Imaging phantom

About: Imaging phantom is a research topic. Over the lifetime, 28170 publications have been published within this topic receiving 510003 citations. The topic is also known as: phantom.

Coronary Artery Calcium: Absolute Quantification in Nonenhanced and Contrast-enhanced Multi–Detector Row CT Studies

Abstract: PURPOSE:(a) To determine the accuracy of multi–detector row computed tomography (CT) in the measurement of the calcium concentration in a cardiac CT calibration phantom and (b) to assess the correlation of a traditional 3-mm section width CT coronary screening protocol and a 1.25-mm section width CT angiography imaging protocol in the quantification of the absolute mass of coronary calcium in patients who underwent both coronary screening and CT angiography with a multi–detector row CT scanner. MATERIALS AND METHODS: A heart phantom containing calcified cylinders was scanned to determine calibration factors and absolute calcium mass. In 50 patients, the variability (value 1 − value 2/mean value 1 − value 2), limit of agreement (±2SD value 1 − value 2), and systematic error (mean value 1 − value 2) of the total amount of coronary calcium calculated at traditional 3-mm section width CT and at 1.25-mm section width CT angiography were determined. RESULTS: The correlation coefficient between the 3-mm section ...

Optical CT reconstruction of 3D dose distributions using the ferrous-benzoic-xylenol (FBX) gel dosimeter.

Abstract: In recent years, magnetic-resonance imaging of gelatin doped with the Fricke solution has been applied to the direct measurement of three-dimensional (3D) radiation dose distributions. However, the 3D dose distribution can also be imaged more economically and efficiently using the method of optical absorptioncomputed tomography. This is accomplished by first preparing a gelatin matrix containing a radiochromic dye and mapping the radiation-induced local change in the optical absorption coefficient. Ferrous–Benzoic–Xylenol (FBX) was the dye of choice for this investigation. The complex formed by Fe 3+ and xylenol orange exhibits a linear change in optical attenuation ( cm −1 ) with radiation dose in the range between 0 and 1000 cGy, and the local concentration of this complex can be probed using a green laser light (λ=543.5 nm). An optical computed tomography(CT) scanner was constructed analogous to a first-generation x-rayCT scanner, using a He–Ne laser, photodiodes, and rotation–translation stages controlled by a personal computer. The optical CT scanner itself can reconstructattenuation coefficients to a baseline accuracy of 2% while yielding dose images accurate to within 5% when other uncertainties are taken into account. Optical tomography is complicated by the reflection and refraction of light rays in the phantom materials, producing a blind spot in the transmission profiles which, results in a significant dose artifact in the reconstructed images. In this report we develop corrections used to reduce this artifact and yield accurate dosimetric maps. We also report the chemical reaction kinetics, the dose sensitivity and spatial resolution (<1 mm3) obtained by optical absorptioncomputed tomography. The article concludes with sample dose distributions produced by “cross-field” 6 MV x-ray beams, including a radiosurgery example.

New diffusion phantoms dedicated to the study and validation of high-angular-resolution diffusion imaging (HARDI) models.

Abstract: We present new diffusion phantoms dedicated to the study and validation of high-angular-resolution diffusion imaging (HARDI) models. The phantom design permits the application of imaging parameters that are typically employed in studies of the human brain. The phantoms were made of small-diameter acrylic fibers, chosen for their high hydrophobicity and flexibility that ensured good control of the phantom geometry. The polyurethane medium was filled under vacuum with an aqueous solution that was previously degassed, doped with gadolinium-tetraazacyclododecanetetraacetic acid (Gd-DOTA), and treated by ultrasonic waves. Two versions of such phantoms were manufactured and tested. The phantom's applicability was demonstrated on an analytical Q-ball model. Numerical simulations were performed to assess the accuracy of the phantom. The phantom data will be made accessible to the community with the objective of analyzing various HARDI models.

Proton radiography as a tool for quality control in proton therapy

Abstract: Proton radiography is investigated for its use as a quality control tool in proton therapy. Images were produced both with range and range uncertainty information of protons passing through phantoms (Alderson phantom and a sheep's head). With the range images the correct positioning of the patient with respect to the beam could be verified. The range uncertainty images were used to quantitatively detect range variations of protons passing through inhomogeneities in the patient. These measurements can be used to indicate critical situations during proton therapy or to determine the safety margin around the tumor volume. With the range information the precision of different calibrations of computer tomography Hounsfield values to relative proton stopping power, used for proton treatment planning, was determined. It is found that the precision in range can be improved by a detailed analysis of the calibration data obtained from tissue-substitute measurements, by a factor of 2.5. The resulting range errors are in the order of the positioning precision (approximately 1 mm).

Errors in the measurements of T2 using multiple-echo MRI techniques. I. Effects of radiofrequency pulse imperfections.

Abstract: In principle, multiple-echo magnetic resonance imaging (MRI) can be used to estimate the spin-spin relaxation time, T2, which can then be used for quantitative tissue characterization. Although multiple echoes can be used to enhance the signal-to-noise ratio in an image, by echo addition, rf pulse imperfections modify the echo amplitudes resulting in significant errors in the estimate of T2. Imperfect 180 degree pulses do not completely invert the transverse magnetization so that the magnitude of the transverse component is reduced and a longitudinal component is generated. Successive application of such imperfect pulses generates many components that interact in a complex manner. The amplitudes of successive echoes are affected whenever the transverse components refocus, whereas the longitudinal components may be rotated into the transverse plane by subsequent pulses and may often add to the image signal or give rise to an image artifact. These effects have been analyzed theoretically and have been demonstrated for a wide range of rf pulse imperfections using both simple and composite pulses, through computer simulations based on the numerical solution of the Bloch equations. The theoretical and simulation results have been substantiated through experiments performed on a mineral oil phantom using a resistive prototype MR scanner operating at 6.35 MHz. In this paper we report the effects of improper pulse amplitude or duration for nonselective rf pulses on resonance. We separately describe the other types of imperfections caused by off-resonance effects and the use of selective pulses.